How this passed through Apple's Mountain Lion testing is beyond me. "If one edits a document, then chooses Save As, then BOTH the edited original document and the copy are saved, thus not only saving a new copy, but silently saving the original with the same changes, thus overwriting the original." Just goes to show: do not mess with my ability to save my stuff. There is no one-size-fits-all for this kind of delicate stuff.

... So, how are we to create shared templates that won't get overwritten the first time someone tries to create a new document from a template?

By "Locking" the file. I think this was a feature since Lion. It would auto-lock the file after not being edited for a while, and it would offer you to duplicate the file. I think you can lock / unlock the file at will, but I haven't tried.

But I agree, this is breaking existing workflows. May be good, may be bad.